The present invention refers to a method of identifying the combustion chamber of a combustion engine that is in the compression stroke. Furthermore, the invention refers to a method and device starting a combustion engine.
In combustion engines having modern electronic ignition systems without high voltage distributors and without camshaft sensors, the proper ignition sequence and the proper injection sequence may not be determined until the engine has been started. After the start as the engine operates, the correct ignition sequence may be determined by means of measuring the ionization current in the cylinder in which the combustion has occurred. According to this prior art, which is described in SE-B-442 345 for instance, a measuring voltage is applied to the ignition circuit in a ground connection between the secondary winding of an ignition coil and a measuring capacitor, which voltage results in a ionization current in the cylinder, and this ionization current is detected in the ground connection by means of a measuring device.
It is known that there is a relationship between the pressure in the combustion chamber of a combustion engine and the spark voltage in the electrode gap of the spark plug. The higher the pressure the higher the spark voltage, which means that the spark voltage is higher when the combustion chamber is in the compression stroke than when it is in the exhaust stroke. Furthermore, since it takes a certain time to build up the voltage resulting in a spark, the spark will occur later, in relation to when the ignition was initiated, when the compression chamber is in a compression stroke than when it is in the exhaust stroke.
The ignition system disclosed in EP-A-0 619 428 refers to an inductive ignition system having two spark plugs connected to a respective end of the secondary winding of an ignition coil. Consequently, the ignition coil will be discharged in such a manner that a voltage having reversed polarity simultaneously is built up across the electrode gap of both the spark plugs. By detecting the spark in both spark plugs and calculating the time difference between the sparks the operating angle of the engine may be determined.
US-A-5 065 729 discloses an inductive electronic ignition system for a combustion engine, which system comprises an ignition coil having a primary winding and two secondary windings each being connected in series to a spark plug forming an electrode gap. The primary winding is connected in series to a transistor controlled by a control unit. Consequently, a spark will be initiated simultaneously in both spark plugs. In order to sense the voltage when the spark occurs, a detector is provided in series with one of the secondary windings and its spark plug, i.e. at the high voltage side. Since the spark voltage increases with increasing compression, it is possible to determine the cylinder that is in the compression stroke and, by means of this knowledge, to control for example the fuel injection during the operation of the engine.
EP-A-0 177 145 discloses a similar ignition system having a device for determining the cylinder that is in the compression stroke in order to synchronize the fuel injection. The device comprises a detector capacitively connected to the high voltage side for determining the spark voltage.
In order to be able to measure the voltage necessary for generating a spark in the electrode gap of a spark plug, a high voltage probe, connected to a measuring instrument disclosing the voltage, for example an oscilloscope, is normally required. The high voltage probe is connected to the high voltage side of the ignition system between the ignition coil and the spark plug. The voltage to be measured depends on the level of the voltage supplied by the ignition system. In a capacitive ignition system the voltage may be as high as 35-40 kV. By measuring such high voltages problems due to flash-over between the measuring equipment and surrounding metal parts of the engine frequently arises.
WO-A-9 221 876 discloses a diagnostic device for detecting electrical defects of a capacitive ignition system of a combustion engine. The ignition system comprises a charging capacitor and a coil having a primary winding and a secondary winding being connected in series to a spark plug forming an electrode gap. The diagnostic device is adapted to estimate the time delay between the ignition signal and the ignition, and this estimate is made by measuring the time period from the triggering, i.e. from initiating the discharge of the charging capacitor, to the moment that the current through the primary winding has achieved a predetermined threshold value. At this threshold value it is assumed that a spark occurs in the electrode gap.
Consequently, WO-A-9 221 876 does not teach how to determine exactly the time period between the triggering and the spark. The time delay estimated is compared to a number of threshold values in order to determine the condition of the ignition system.
DE-A-3 041 498 discloses a conventional ignition system having a measuring and regulating device for determining the time delay between the triggering and the spark, i.e. from an ignition control signal flank initiating the ignition to the occurrence of a spark. The spark is detected by sensing the negative going edge of the voltage at the measuring and regulating device. The determined time delay is utilized to adjust the ignition point of time.